In Vann U.S. Pat. No. 4,040,482, U.S. Pat. No. 4,066,282 and U.S. Pat. No. 3,966,236, it is pointed out that one often can foresee that the lower part of a tool string or tubing string subsequently must be disconnected from the remainder of the string. This is especially so in well completion work wherein the lower portion of the tubing string must sometimes be severed by employment of explosive devices, and the severed lower portion of the string dropped to the bottom of the hole.
Various different tubing release couplings have been proposed as evidenced by the above mentioned patents. In the prior art tubing release couplings, it is necessary to run a tool downhole on the end of a slick line or wireline in order to mechanically release the coupling, and this is objectionable for several reasons. There is always a possibility that the wireline tool could become stuck downhole in the borehole, thereby necessitating a costly fishing job. Moreover, it is often difficult to mechanically shift prior art release mechanisms with a wireline tool in deviated well bores that are not vertical or not straight. Some well bores have multiple curves, such as S-shapes or the like, for example, slanting 50 degrees from vertical, followed by slanting 20 or 30 degrees in another direction. Other well bores might be relatively straight, but highly angled or deviated from vertical. In such curved or highly angled well bores, physically manipulating the prior art wireline-type release tools in order to engage the release mechanism of the releasable coupling is often a problem. In particular, it is most difficult to pass a wireline tool down a deviated well since the wireline has no rigidity. In addition, sometimes such prior art releasable couplings are accidentally or prematurely tripped or released by other tools, such as logging tools, being run up and down the well bore through the releasable coupling, both in such curved or deviated well bores and in well bores that are relatively straight and vertical, which again would necessitate a costly fishing job.
A release coupling which avoids the difficulties experienced with prior art releasable couplings and which is manipulated by passing a sealing member down the axial passageway of the pipe string and thereafter applying pressure through the axial passageway above the sealing member is the subject of the present invention.